Method for suppressing dust emissions from bulk solids

ABSTRACT

A method for controlling fugitive dust emissions from bulk granular or powdered solids is disclosed. Fugitive dust emissions are controlled by applying an aqueous, foamed solution including a water-soluble cationic polymer to dust producing bulk, granular or powdered solids. The cationic polymer is incorporated into an aqueous foam comprising anionic, amphoteric or cationic foaming agents.

FIELD OF THE INVENTION

The present invention relates to methods of suppressing fugitive dustemissions by applying an aqueous foamed solution including awater-soluble cationic polymer to dust producing bulk solids. Moreparticularly, the present invention relates to methods for providingresidual or long term fugitive dust control for bulk granular orpowdered solids with an aqueous foamed solution including awater-soluble cationic polymer. The aqueous solution may be foamed byincorporation therein of an anionic, amphoteric or cationic foamingagent.

BACKGROUND OF THE INVENTION

Dust dissemination poses safety, health, and environmental problems inmany commercial environments. For instance, in many industries, thetransportation handling and storage of bulk solids is common as inindustries such as mining, mineral processing, agricultural, power,steel, paper, etc. One major problem associated with bulk solids is dustgeneration and the control of fugitive dust emissions.

Industrial sources of fugitive dust include open operations, leaks andspills, storage, disposal, transit or poor housekeeping of sundry finelydivided solid particulates. The iron and steel industries are repletewith examples of the above enumerated categories. Wind erosion ofexposed masses of particulate matter such as coal or mine mill tailings,fertilizer, etc., causes both air pollution and economic waste.Detrimental effects on health and cleanliness result where these fineparticles are carried aloft by the winds.

A typical method for controlling the dust is to apply a water spray.However, water sprays only control dust for a short period of timedepending upon environmental conditions. The application of the sprayhas to be repeated frequently to provide ongoing dust control. U.S. Pat.No. 3,954,662 discloses aqueous foamable compositions and their use tosuppress coal dust. The composition contains water, an interpolymer of apolymerizable vinyl ester and a partial ester compoundinterpolymerizable with the vinyl ester, and a detergent wetting agent.The interpolymer binds coal dust and keeps the dust particlesencapsulated after the foam has collapsed.

U.S. Pat. No. 4,087,572 discloses a combination of an organic polymerlatex such as a styrene-butadiene interpolymer and a silicone applied tothe surface of a coal pile or other mass of finely divided particulatematerials. In addition, a wetting agent may be incorporated to preventpremature coagulation. The combination is applied as an aqueous mixturesuch as by spraying.

U.S. Pat. No. 4,551,261 discloses the suppression of dust with anaqueous foam comprising a foaming agent and an elastomeric waterinsoluble polymer. The foam provides immediate dust suppression andeases application. The polymer coats the material and continues tosuppress dust generation during handling of the material after the foamhas collapsed.

U.S. Pat. No. 4,594,268 discloses the use of at least one methacrylatepolymer for dust suppression. The methacrylate polymer provides dustsuppression when applied to a wide variety of materials. Afterapplication, the polymer provides a tacky, water resistant coating whicheffectively prevents dusting while additionally acting as an anti-freezeagent.

U.S. Pat. No. 4,801,635 discloses a combination of water soluble anionicacrylic polymers and nonionic glycol polymers and anionic and nonionicsurfactants useful for the control of dust emissions into theenvironment.

U.S. Pat. No. 4,780,233 discloses a method and composition forcontrolling fugitive dust particles which comprises an oil containingdust control treatment including a small amount of a water insolubleelastomeric polymer. The inclusion of a small amount of elastomersignificantly improves the dust control performance. The composition canbe applied as a spray or foam.

SUMMARY OF THE INVENTION

The present invention relates to improved methods and compositions forcontrolling fugitive dust emissions from bulk, granular or powderedsolids. Fugitive dust emissions are controlled by applying an aqueous,foamed solution including a water-soluble cationic polymer to dustproducing bulk, granular or powdered solids. The cationic polymer isincorporated into an aqueous foam comprising anionic, amphoteric orcationic foaming agents. Wetting agents such as nonionic ethoxylatedalcohols may also be included for improved wetting of the solidsubstrate. For materials with a propensity for caking or similarhandling problems, anti-caking agents or flow aids may be included suchas cationic amines, tallow primary amines, mineral oils, etc.

The dust control methods and compositions of the present invention areparticularly effective at controlling fugitive dust dissemination inurea processing and handling. In the treatment of urea for dust controlin accordance with the present invention, anti-caking agents or flowaids are particularly desirable due to the tendency of urea to cake. Thecompositions and methods of the present invention provide effectiveresidual or long term dust control.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The dust control composition of the present invention is an aqueoussolution of a water soluble cationic polymer. These materials may beselected from a wide variety of water-soluble cationic polymers. Thepolymers may be either addition polymers or condensation polymers. Mostsynthetic cationic polyelectrolytes are polyamine and polyquaternaryammonium salts although non-nitrogen based cationic species are known.Polyamines and polyquaternary amines can be prepared by free-radicalchain polymerization, epoxide-addition reactions, condensationpolymerization, and reactions on polymer backbones. Polymers of thistype are described in Roe, U.S. Pat. No. 4,426,409, the disclosure ofwhich is incorporated herein by reference. Polyamines and polyquaternaryanions are also discussed at pp 489-507 of The Encyclopedia of PolymerScience and Engineering, Vol. 11, Second Edition, 1988.

The treatment solution is preferably supplied as a concentrate which isdiluted prior to application as a foam. The treatment concentration, inpercent cationic polymer by weight in the foam, can range from about0.01 to 10.0% and is preferably from about 0.1 to 1.0%. The feed rate offoam onto the substrate, on a weight % basis, can range from about 0.05to 5.0% and is preferably from about 0.1 to 1.0%.

The dust control composition of the present invention is applied as afoam. The foam for the dust control treatment may be foamed and appliedvia conventional techniques such as those disclosed in U.S. Pat. No.4,400,220 (Cole), the contents of which are hereby incorporated byreference. Accordingly, a suitable foaming agent is included.

Cationic and amphoteric foaming agents are preferred. Amphoteric foamingagents such as coco amido sulfobetaines are especially preferred. Suchfoaming agents are available commercially. For example, EMCOL 6825available from Witco Chemical Corporation. In general, cationic polymerscannot be foamed with anionic foaming agents. However, the inventor ofthe present invention discovered that the cationic polymer ofdiethylenetriamine/adipic acid/epichlorohydrin can be foamed with ananionic foaming agent comprising a blend of the sodium salts of C14-C16alpha olefin sulfonate and alkyl ether sulfate. Exemplary commercialproducts are Bioterg AS-40 and Steol KS-460 available from StepanChemical Co. It is believed, therefore, that other anionic foamingagents may also be capable of foaming this and other cationic polymers.

The present invention will now be described with respect to a number ofspecific example which are to be regarded solely as illustrative and notas restricting the scope of the invention.

EXAMPLES

Laboratory testing was conducted to determine the dust control effectsof water-soluble cationic polymer compositions on feed grade urea. Thepolymers were applied to the urea as aqueous foams with cationic andanionic foaming agents. The effectiveness was tested by measuring therelative dusting index (RDI) and percent dust suppression (% DS). TheRDI of treated and untreated control samples was measured in alaboratory dust chamber equipped with an opacity monitor. The opacitymonitor generated an opacity curve as a function of time, measured afterintroduction of the treated samples into the dust chamber. The relativedustiness index was measured as the area under the opacity curve. Thepercent Dust Suppression was a calculation based on the RelativeDustiness Index for untreated versus treated materials. All samples wereaged for 24 hours at 20° C. and 50% relative humidity prior to testing.

Table I summarizes the results of testing showing the large decrease inRDI and relatively high % DS numbers for a variety of water-solublecationic polymer treatments in accordance with the present invention.

                  TABLE I                                                         ______________________________________                                        Effects of Foamed Cationic Polymers on                                        Relative Dustiness (RDI) of Feed Grade Urea                                           Concentration                                                                 (% Polymer  Feed Rate                                                 Treatment                                                                             in Foam)    (Wt % of Foam)                                                                             RDI   % DS                                   ______________________________________                                        Control --          --           11.1  --                                     Control --          --           12.2  --                                     A       0.25        0.22         2.3   80.3                                   B       0.25        0.23         2.5   78.6                                   C       0.25        0.22         2.8   76.1                                   D       0.25        0.23         4.1   65.0                                   ______________________________________                                         Legend:                                                                       A: Melamine/formaldehyde polymer and coco amido sulfobetaine cationic         foaming agent.                                                                B: diallyldimethyl ammonium chloride polymer and coco amido sulfobetaine      cationic foaming agent.                                                       C: diethylenetriamine/adipic acid/epichlorohydrin polymer and coca amido      sulfobetaine cationic foaming agent.                                          D: diethylenetriamine/adipic acid/epichlorohydrin polymer and an anionic      foaming agent.                                                           

As shown in Table I foamed cationic polymers provide effective dustsuppression.

While the present invention has been described with respect toparticular examples, it is apparent that numerous other forms andmodifications of the invention will be obvious to those skilled in theart. The appended claims and this invention should be construed to coverall such obvious forms and modifications which are within the spirit andscope of the present invention.

What is claimed is:
 1. A method of suppressing the dissemination offugitive dust particles into the atmosphere from urea comprisingcontacting the urea with a dust suppressing amount of a foam comprisingwater, foaming agent, and a water-soluble cationic polymer.
 2. Themethod of claim 1 wherein said cationic polymer is selected from thegroup consisting of polyamines and polyquaternary ammonium salts.
 3. Themethod of claim 1 wherein said water-soluble cationic polymer isselected from the group consisting of melamine/formaldehyde polymer,diallyldimethyl ammonium chloride polymer, and diethylenetriamine/adipicacid/epichlorohydrin polymer.
 4. The method of claim 1 wherein saidfoaming agent is an anionic, amphoteric or cationic foaming agent. 5.The method of claim 1 wherein said water-soluble cationic polymer is adiethylenetriamine/adipic acid/epichlorohydrin polymer and said foamgenerating agent is an anionic foaming agent comprising the sodium saltsof alkyl ether sulfate and C14-C16 alpha olefin sulfonate.
 6. The methodof claim 1 wherein said foam further includes a wetting agent.
 7. Themethod of claim 1 wherein said foam further includes a wetting agent. 8.A method of suppressing fugitive dust dissemination from urea comprisingcontacting urea with a dust suppressing amount of an aqueous foamsolution containing a foam generating agent and a water-soluble cationicpolymer.
 9. The method of claim 8 wherein said water-soluble cationicpolymer is selected from a group consisting of polyamines andpolyquaternary ammonium salts.
 10. The method of claim 8 wherein saidwater-soluble cationic polymer is selected from the group consisting ofmelamine/formaldehyde polymer, diallyldimethyl ammonium chloridepolymer, and diethylenetriamine/adipic acid/epichlorohydrin polymer. 11.The method of claim 8 wherein said foam generating agent is an anionicamphoteric or cationic foaming agent.
 12. A method of suppressingfugitive dust dissemination comprising contacting a dust producingmaterial with a dust suppressing amount of an aqueous foam solutioncontaining an anionic foaming agent comprising the sodium salts of alkylether sulfate and C14-C16 alpha olefin sulfonate and a water solublecationic polymer of diethylenetriamine/adipic acid/epichlorohydrin. 13.The method of claim 12 wherein the dust producing material is urea.